Amid a tabloid story that Oprah Winfrey was "ambushed" by her "secret son," Calvin Mitchell, outside the Ed Sullivan Theater in New York earlier this month, the media mogul is setting the record straight in an exclusive interview with Entertainment Tonight's Nancy O'Dell.

"I met Calvin around the early '90s, I think it was 1992. I was doing a film for television called There Are No Children Here," Oprah told ET, confirming that Calvin is not her birth son. "We were shooting in the projects in Chicago and I was sitting on set during a break, and this cute little sparkly-eyed boy came underneath the yellow tape to hand me a soda. I was so charmed by him that I started talking to him about his family, his school life, and found out that he was in a situation where his mother didn't have a job and they were stuck in the projects."

Oprah went to explain that she took it upon herself to help the family move out of the projects, find employment for Calvin's mother, and enroll Calvin in a local private school. When the principal called to inform her that Calvin hadn't been attending class, Oprah and her partner, Stedman Graham, paid the family a visit. The family told her that they weren't able to wake up on time to get Calvin to school.

"We realized they don't have any clocks in the house," she said. "We went out, Stedman and I, went to K-Mart that moment, got a bag full of clocks, came back to the house, taught them how to set the alarm and all that."

Oprah said that Calvin was eventually expelled from the school.

"I had a long conversation with him about how disappointed I was but I was going to give him another chance," she continued. "I found a school in Mississippi that was a private boarding school because I thought if I could remove him from the environment that he'd been accustomed to growing up in, that maybe that would be helpful to him."

Oprah told ET that, at 16 years old, Calvin said that he couldn't stay at the boarding school because "the teachers didn't like him."

"I said, 'Calvin, this is the moment. This is a seminal moment for you. I know you are 16 and can't see the road ahead, but if you leave this school and refuse to get an education -- I have tried to offer you an education twice -- there isn't another school I can put you in. If you leave this school, I am done. There is nothing else I can do.' ... And that was my last conversation with Calvin in the early '90s."

Oprah says that she didn't immediately recognize Calvin when he approached her after a taping of The Late Show With Stephen Colbert earlier this month, but attempted to make contact with him after their run-in. She had already suspected that he told his story to the tabloids, after she was asked by a media outlet for comment about her "secret son."

"I could see the little boy in his eyes, even though time has changed a lot for him, and I said to him, 'What are you doing? Why did you go to the tabloids?'" Oprah said.

"As I left, and he was looking so forlorn, he was like, 'Can I speak to you?' So I said to somebody on my team, 'Will somebody get Calvin's number so I can contact him later?' I didn't realize the whole thing was a setup.

"When I realized the whole thing was a setup, I was no longer interested in speaking to him," she continued, noting that she's not hurt, but is "disappointed."

Oprah also said that it was her experience with Calvin that inspired her to open her Leadership Academy for Girls in 2007.

"I learned from that experience, if you really want to change somebody's life, you gotta be able to spend enough time with them to change the way they think about what their life can be," she said. "It isn't enough to give a person a new life or money or a new car, you have to teach them how to fish themselves."

In ET's last interview with Oprah, she got candid about her "next level" new project. Watch below.